Project Summary The proposed study aims to determine the optimal levels of treatment intensity of a word learning intervention for young school-age children with language impairment (LI; 5- 6-years-old) by systematically manipulating the treatment dose and frequency children receive. Cumulative intensity is the product of treatment dose (the number of treatment exposures) and treatment frequency (the number of treatment sessions) and both contribute to intervention effectiveness. To date, there are few studies that have examined the interplay of dose and frequency to determine optimal levels to affect change, and the extent to which there may be a threshold, or a level after which significant gains diminish. Within the framework of distributed learning theory (Cepeda et al., 2006), the proposed study will determine the optimal level of treatment intensity of an efficacious work learning intervention (Justice et al., 2005; Storkel et al., 2017; Voelmle and Storkel, 2017) designed to improve the vocabulary knowledge of children with LI. The first aim, determining the optimal number of treatment sessions, is proposed to determine differences between treatment provided within a distributed, or spaced, schedule (high-frequency, 4 times a week) and a consolidated, or massed, treatment session (low-frequency, 1 time a week). The second aim of this study, identifying optimal dosage, will determine the number of times a word should be targeted, using rich instructive strategies, within each frequency condition. Preliminary studies of children with LI in the public schools suggest that children with LI who received high frequency/low dose treatment (or low frequency/high dose) made better gains over time than children receiving the extremes (Schmitt et al., 2017). These findings are correlational in nature; the current study aims to manipulate both parameters of intensity (dose and frequency) to determine the optimal levels of treatment intensity. This study?s third aim will examine the point at which increases in dose with respect to frequency (i.e., more word exposures) are no longer advantageous to children?s outcomes. To address these aims, the proposed study will recruit 180 children with LI over three consecutive years. Participants will be randomized into one of two frequency conditions (high vs. low) which will determine how frequently they receive treatment (once/week or four times/week). Within those treatment sessions, children will learn 60 words; each word will be randomly assigned to one of six possible dose conditions (0 ? 20 word exposures). Student interns will deliver the manualized word learning intervention in one-on-one sessions for 10 weeks in the summer. Although frequency conditions differ, all children will receive 120 minutes of therapy per week. Children?s learning of the novel words, as well as their overall vocabulary skills will be measured at three time points: pre-treatment, immediate post-treatment, and 6-months post treatment to assess the impact of the treatment and intensity regimens on short and long-term outcomes. Findings will immediately inform clinical practice regarding quantity of therapy needed for improving the vocabulary skills of children with LI.